This invention relates generally to an improved base construction for various type high intensity arc discharge lamps and more particularly to providing simpler means for permanently securing a screw type base member directly to the outer lamp envelope.
High intensity arc discharge lamps of various types are now globally employed as a source of highly efficient white and colored illumination in both indoor and outdoor applications. Both mercury vapor and metal halide types of said lamps conventionally employ a tubular arc tube of light transmissive vitreous material as an inner light source which is hermetically sealed within an outer vitreous lamp envelope. The arc tube comprises a hermetically sealed envelope, which can be quartz glass having thermionic electrodes at opposite ends in pinch seal regions and further contains a gaseous discharge medium which includes mercury. The gaseous discharge medium can further contain alkali metal and/or alkaline earth metal additives to form an amalgam with mercury. Addition of the latter additives in metal halide lamps has been found to enhance the color of light output as well as increase its efficiency. The general construction of such type lamps is further disclosed in U.S. Pat. Nos. 4,007,397; 4,581,557; and 5,055,740 to include the conventional use of a screw type conductive base member for operation in existing socket fixtures.
A common construction in prior art lamps of this type includes an inner hollow shell member affixed to the outer lamp envelope which is threaded into an outer shell member. A pair of lamp inlead conductors emerging from the outer lamp envelope are terminated by connection to the outer metal shell member with one of said inlead conductors being electrically isolated therefrom in the customary manner. Understandably such requirement for a multi-shell base assembly complicates lamp manufacture as well as increases lamp cost. A need to carefully control the physical tolerances in both size and shape of the individual shell members in such base assembly for the high speed lamp manufacture now being carried out represents still another problem associated with the prior art base construction.
Accordingly, one object of the present invention is to provide a more simple base construction for high intensity arc discharge lamps.
It is another object of the present invention to provide a base construction for high intensity arc discharge lamps which is less subject to control of physical tolerances between the individual base components.
A still further object of the present invention is to reduce material costs for a base construction in such type lamps.
Still another object of the present invention is to provide a relatively simple modification in otherwise conventional lamp manufacture needed for the basing of a high intensity arc discharge lamp.
These and still further object of the present invention will become more apparent upon considering the following detailed description for the present invention.